Packers are used downhole to isolate different zones. Some packers are made to be removed at a later time after being set in the well for what could be fairly long time periods. These packers are referred to as retrievable. They generally feature slips actuated by cones that are moved under the slips to move them out radially to support the packer. A sealing element assembly is between the upper and lower slips. In order to retrieve such packers the cone that wedges in a slip assembly has to be retracted from under the slip that it formerly wedged against a tubular. Usually, on mechanical set packers the mandrel is manipulated by tubing string rotation so that it pulls the cone out from under the upper slip assembly to allow the sealing element to relax as the packer extends so that it can then be pulled out.
Retrievable packers can be pressure set with applied pressure moving a piston that brings the cones of the slips together to move them out while compressing the sealing element. Mechanically set packers usually have drag blocks, which are spring energized members to give temporary support to the packer outer housing as a tubing string connected to the mandrel is manipulated by rotation. One style uses a j-slot so that the tubing can be turned and set down and the string weight applied to the mandrel sets the packer as the outer housing is supported on the drag blocks.
Pressure set retrievable packers, in the past, have recognized the need for a debris barrier above the upper slips. The solution offered in U.S. Pat. Nos. 6,302,217 and 6,112,811 involves a rubber ring on a slip ramp so that when a pressurized piston gets the packer parts moving, the upper slip riding on its respective ramp pushes out a rubber ring and wedges it into a gap against the surrounding tubular after it crests the slip ramp. In a variation, the debris barrier is initially held in a groove above and below a slip assembly and setting the slips with a pressurized piston forces the debris barrier ring out of its run in groove and up the slip ramp where it hopefully becomes wedged against the surrounding tubular.
While the design appears to address the problem on paper, it has many practical limitations. Directly forcing a ring to enlarge in diameter and move up an inclined ramp several issues are encountered. The ring as it enlarges in diameter can roll about its circumferential center line. If this happens it will move up the ramp unevenly leaving less than 360 protection and is also likely to rip before becoming wedged against the surrounding tubular. Another concern from this type of wedging action is that the debris barrier can be subjected to a wedging force that can be sufficient to extrude it, which can also result in a tear. If the ring is dependent of slip movement to ramp it out, any failure along the ramp can result in pieces of the ring acting as a brake on movement of the slip assembly up the ramp. As a result, a less than optimal grip is obtained and the set packer is exposed to the possibility of loss of grip.
While debris barriers have been offered in pressure set packers that rely on driving a setting piston to actuate the slips and sealing element, such barriers have not been available on mechanical set packers that are also designed to be retrievable. The present invention addresses this need in such packers with a design that can be simply retrofit on existing mechanical set retrievable packers. The design spaces the debris barrier from the slip assembly and keeps it energized while the packer is set. The barrier is retracted for run in and can be readily extended to bridge the gap to the surrounding tubular when the packer is set. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings, recognizing that the full scope of the invention is indicated in the attached claims.